The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
The most common method of generating compressive residual stress in the surface of a material is shot peening, where small particles or balls (shot) are impacted against the target material to deform the surface. The shot is typically propelled with compressed air using automated equipment to move the peening nozzle over the surface of the part to be peened. The shot, frequently steel or ceramic, is usually accelerated to 50-100 m/s by the compressed air and strikes the surface with enough energy to deform the top layer of material beyond its elastic limit.
This plastically deformed surface induces residual compressive stresses in the material as the material underneath, which is not plastically deformed, tries to push the plastically deformed material back into its original volume. This “pushing” is the compressive stress that is a beneficial material property.
Variations on this method include striking the surface with particles spun off from a rotating wheel, low plasticity burnishing with a ball that is hydraulically pressed into the surface as it rolls across the part, and laser shock peening (LSP).
Cavitation peening is another method that involves shooting a high-pressure liquid jet against the target material in such a manner that cavitation bubbles collapse and shock waves pass into the material. Cavitation peening is generally performed with the liquid jet and the target material both submerged in a liquid. The shock waves generate compressive residual stresses in the target material similar to the other methods described above. However, cavitation peening has traditionally presented several shortcomings, such as limited stress depth, limited stress intensity and limited process rates, and has been known to cause damage to the surface of the peened material.
Examples of cleaning or stripping methods may include removal of scale, oxides, chrome coatings, thermal barrier coatings, or others. Examples of surface roughening applications include roughening metals or ceramics to create a desirable bonding surface geometry for coatings or bonding agents.